1. Field of the Invention
The present invention relates to a method of yielding concentrated ethanol from an ethanol water solution yielded from ethanol fermentation of a saccharide water solution generated by saccharification of biomass containing lignocellulose by enzyme.
2. Description of the Related Art
In recent years, from the viewpoint of preventing global warming, it has been called on to reduce emission amount of carbon dioxide which is considered to be one of the reasons of global warming. Therefore, there has been considered to use a mixed fuel of ethanol and a liquid hydrocarbon compound such as gasoline as a vehicle fuel.
The ethanol can be yielded from fermentation of a plant material, for example, an agricultural crop such as sugar cane, corn or the like. Since the plant itself, the raw material of the plant material, has absorbed carbon dioxide via photosynthesis, even though the ethanol produced from the plant material is combusted, the emission amount of carbon dioxide is equal to the amount of carbon dioxide absorbed by the plant itself. In other words, the summed emission amount of carbon dioxide can be made theoretically equal to zero, which is the so-called carbon neutral effect.
However, if sugar cane, corn and the like are consumed in a large amount as the raw materials for preparing ethanol, there is a problem that the amount thereof supplied as food would be decreased. In this regard, there has been considered a technology to produce ethanol by using an inedible biomass containing lignocellulose as a substituent to the plant material such as sugar cane, corn or the like. As examples of the biomass containing lignocellulose, wood, rice straw, haulm, bamboo, pulp and waste materials originated therefrom, such as waste paper, may be given.
As a production method for ethanol, there has bee known a method as disclosed in Japanese Patent Laid-Open No. 2006-136263, Japanese Patent Laid-Open No. 2006-88136, in which biomass containing lignocellulose is saccharifized by enzyme by adding diastatic enzyme thereto so as to generate saccharide aqueous solution, and further the saccharide aqueous solution is added with ethanol fermentative bacteria to carry out ethanol fermentation, so as to yield ethanol water solution.
However, the ethanol water solution yielded from the above-mentioned ethanol production method is dilute, since the concentration of ethanol is ranged from 0.5 to 5.0 wt %. Therefore, there is a problem that it is difficult to use the same for automotive fuel as it is. Therefore, it is conceivable to yield concentrated ethanol by separating water from the ethanol water solution with pervaporation method using water separation membrane.
However, in the ethanol water solution concentrating method mentioned above, there is a disadvantage that the concentrated ethanol is still dilute at 3.0 to 5.5 wt %, even after separating a part of water from the ethanol water solution.